Voltage controlled AVR LFO with variable symmetry

Posted on October 7, 2021 by Harald

**Voltage controlled AVR LFO: Front view**

This is an old project dated back to December 2017. It was intended to learn some basics about the hard- and software of the ATMEGA series from AVR. It is kept simple. Just three analog inputs, one interrupt input and PWM output with filter are used. It is up to you what software you want to run on it. Here I made a simple voltage controlled VCO with variable symmetry. Speed, waveform and symmetry are voltage controlled. So you can change the triangle from ramp up to triangle to ramp down. Or make one halve of the sine very small. See screenshots below. This software was mainly written to test the hardware. To my surprise it worked sufficiently well for a LFO. So I leave it as is for the moment. No fancy accumulation with fixed point arithmetic and increment interpolation. Of course there is a lot room for improving the software. I know.

Specs and features

Voltage control for speed, waveform, symmetry
Bipolar and unipolar output
Square, triangle, sine, ramp up, ramp down waveform
20MHz crystal
19.5kHz PWM 10bit resolution
Runs on +/-15V and +/-12V
Power consumption around 30mA positive, 5mA negative rail

The documentation and the Gerber files for download can be found in my website.

**Voltage controlled AVR LFO: schematic 01**

**Voltage controlled AVR LFO: schematic 02**

**Voltage controlled AVR LFO: Populated PCB**

**Voltage controlled AVR LFO: Screenshot waveform**

Pitch to voltage converter

Posted on December 14, 2020 by Harald

This is the software driven replacement for my all hardware pitch to voltage converter from my Shakuhachi to Synth project. The software driven approach has the advantage of easily adaption for different frequency ranges. In my case it is the range of the Shakuhachi. To change the range just adapt the software. It is completely temperature independent. The needed input is a pulse train derived from your original signal. You can use my Signal to Trigger converter to provide the pulse train. An offset voltage is added to the V/Oct output to fit the needs of your VCO (Synthesizer).

Specs and features

Software driven pitch to voltage converter
12bit resolution
V/Oct output
Offset CV Fine and coarse adjustment
Runs on +/-15V and +/-12V
Power consumption around 45mA positive rail, 15mA negative rail

The documentation and the Gerber files for download can be found in my website.

**Pitch to voltage converter: Microprocessor board**

**Pitch to voltage converter: Control board**

The incoming pulse train is feed to the microprocessor. IC1 (301-F) prevents the microprocessor from negative inputs. Zener D2 prevents from overvoltage. The trigger starts an internal timer of the microprocessor in input capture interrupt mode. The ticks are counted and the count is then looked up in a table. The lookup table provides the values for the V/Oct conversion. The read value is the send to the DAC MCP4921 which is follwed by a low pass (IC1A, 301-B)). IC2A (301-F) adds the offset voltage and IC2B (301-F) corrects the phase.

Pitch to Voltage converter: Populated PCB's — **Pitch to Voltage converter: Populated PCB’s**

**Pitch to Voltage converter: Side view**

Clock Divider with prime numbers

Posted on April 5, 2018 by Harald

Clock Divider with prime numbers

This clock divider divides the incoming clock signal down to the prime numbers /11, /13, /17, …. /31. The output is a 5V positive pulse. The length of the incoming pulse is kept. The trigger is on the rising edge of the incoming signal. The reset input can be used for syncing with other clocks. All outputs are buffered and brought out parallel with LED signaling the pulse.
Specs and features
• Regular input clock/square wave +5V
• Input signal divided by prime numbers
• Output +5V pulse with the length of the input signal (pulse)
• Runs with +15V/-15V or +12V/-12V (with minor changes)

The documentation for download can be found in my website.

Clock Divider with prime numbers, schematic

Most work is done by the microprocessor. The micro takes care of the input and output timing. All outputs are independently buffered. The clock is made visible with LED.

Clock Divider with prime numbers, populated PCB

Clock Divider with prime numbers, rear view

Leap 42.3 broken AVR toolchain after update

Posted on January 11, 2018 by Harald

After a recent update the AVR Toolchain did nor longer work. It turned out that some links are missing. You can repair that easily. Login as root and then goto:

cd /opt/cross/avr

Now set the limks:

ln -s /usr/avr/sys-root/include include
ln -s /usr/avr/sys-root/lib lib
ln -s /usr/avr/sys-root/man man
ln -s /usr/avr/sys-root/share share
The toolchain should work again.

VocLog

Analog Synthesizer DIY

Category Archives: AVR

Voltage controlled AVR LFO with variable symmetry

Specs and features

Pitch to voltage converter

Specs and features

Clock Divider with prime numbers

Leap 42.3 broken AVR toolchain after update